1. Field of the Invention
This invention relates to mass spectrometers and, more particularly, to a cryogenic collimator for collimating pyrolysis fragments prior to ionizing the pyrolysis fragments for analysis in the mass spectrometer.
2. The Prior Art
Mass spectrometers are well known in the art and are used to analyze ionized pyrolysis fragments produced upon pyrolysis of a sample. The ionization step in the foregoing procedure occurs in an ionization center located in an evacuated chamber. However, it has been known that the pyrolysis step generates gaseous products and causes a pressure rise within the evacuated chamber of several orders of magnitude of pressure increase. Accordingly, one researcher has included a cryogenic plate adjacent the ionization center opposite the pyrolysis unit. The cryogenic plate acts as a trap for pyrolysis fragments thereby removing those pyrolysis fragments from contributing to a pressure increase in the evacuated chamber.
In one prior art device, pyrolysis occurs in an enlarged, evacuated vessel having a small outlet directed toward the ionization center. Pyrolysis of a sample inside the vessel results in a substantial pressure increase so that the pyrolysis products are directed as a jet into the ionization center. However, it has been recently discovered that secondary collisions occur between pyrolysis fragments and that these secondary conditions result in secondary reactions which produce compounds that were not present in the original sample. These spurious or secondary compounds interfere with the accuracy of the reading obtained from the mass spectrometer.
In view of the foregoing, it would be an advancement in the art to provide an apparatus and method for reducing the number of secondary collisions in pyrolysis fragments from a pyrolyzed sample. It would also be an advancement in the art to provide an apparatus and method for collimating pyrolysis fragments directly from the pyrolyzed sample. Such an invention is disclosed and claimed herein.